Various problems exist with gas burner ignitors. With small capacity burners in the range of 50 to 250,000 btu per hour, the gas from the burner nozzle mixes with exterior air to form an air/gas mixture which is directed against an ignitor element, such as a hot surface ignitor which is usually heated to a temperature of about 2300.degree. F. Because exterior air is often cool, the hot surface of the ignitor is cooled by this exterior air and it therefore takes more time for the element to reach its ignition temperature.
Several methods are used to insure ignition.
A) The entire ignition sequence is restarted including pre and post purge. This slowly heats the local ignition area to facilitate ignition. Unfortunately, if ignition still does not take place, a manual reset or a shutdown is initiated by the burner control. This method wastes electrical and gas energy and can lead to service calls that have to be charged to the user. PA1 B) After the standard pre-purge of the combustion chamber, the fan is stopped. The gas valve slowly opens. Since there is no air circulation, a controlled explosion is initiated and the fan restarts when a flame is detected and then the gas valve fully opens. This controlled explosion generates a sound that is audible outside as well as near the unit. The explosion makes a sound which causes an inconvenience to the users as they perceive that the burner is malfunctioning and that there might be danger of explosion. To control this problem fans are used to purge the combustion gas when ignition does to take place. This necessitates the use of controls to cycle the fans and the gas valve.
With larger burners having capacities of 250,000 to 400,000 btu and above, the use of a modulator system is employed whereby to modulate the air to create small volumes of gas/air mixture which increases slowly. Such systems utilize modulating gas valves or step gas valves as well as variable speed air supplies and complex electronic ignition controls. Other system use a pilot that is ignited intermittently or continuously to ensure main burner ignition. Like the cold air problem the high volume of air-gas in the mixture and its velocity cools the ignitor element or the spark does not have sufficient time to be in contact with the gas-air mixture and thus ignition is not possible or instantaneous. The result is usually a restart of the ignition protocol: pre-purge, actuate ignition (hot surface or spark), open gas valve, check for flame, fully open gas valve or if no flame is detected, post purge and repeat the sequence.